A speaker device has conventionally been known where a plurality of ultrasonic vibrators are arranged in an array shape to have a directivity thereof. Such a speaker device is also called a parametric array speaker and applies an ultrasonic voltage that is modulated by a sound signal in an audible wave band to a plurality of ultrasonic vibration elements so that it is possible to generate an audible sound in a particular direction (see, for example, Japanese Patent Application Publication No. 2008-022347).
For such a speaker that has a so-called narrow directivity, one is also proposed that includes a vibration element in at least one site on a panel-type vibration plate and generates a standing wave on the vibration plate due to vibration of such a vibrator in such a manner that each of antinodes of such a standing wave is a sound radiation unit and radiates a sound wave that has a directivity in a predetermined direction with respect to a panel surface.
Generally, in such a speaker device, a sound pressure level of an audible sound to be output is increased with increasing a voltage that is applied to a vibration element. However, in a speaker device as described above, an applicable voltage is limited from a viewpoint of durability of a vibration element. Accordingly, it is desired that an applied voltage is reduced and a sound pressure level of an audible sound to be output is raised.